Most people believe themselves to be good. Unfortunately, they are comparing themselves against the standard of man, and not the standard of God. The day you stand before God, you are going to be judged by His standard alone. Ask yourself these questions and see how well you compare to God's law (the 10 Commandments). Be honest with yourself and God.
Have you ever told a lie? Even telling one lie makes you a liar.
Have you ever taken something that wasn't yours? The value is irrelevant, and how long ago you did it doesn't matter either. Time doesn't forgive sin.
Have you ever looked at someone with lust in your heart? Jesus said, "Whoever looks upon a woman to lust after her has committed adultery already with her in his heart."
The Bible says that God will punish all liars, thieves, and adulterers, etc. He will even judge our words and thoughts. On Judgment Day, will you be found innocent or guilty of breaking His Law? You may think that because God is good, He will therefore overlook your sins. But it is because of His goodness that He must give justice to liars, thieves, and adulterers.
Imagine you are in a courtroom standing before a judge, guilty of some very serious crimes. The judge asks you if you have anything to say and you tell him that you are very sorry and promise not to commit any more crimes. You also tell him you know him to be a good man, and you then beg him to overlook your crimes. If he's a good judge, he is going to see that justice is done in his courtroom, and that you pay the price for your crimes. Only a corrupt judge would turn a blind eye to crime, and God is not a corrupt judge. By his very nature God must punish liars, thieves, adulterers, idolaters, and everyone that has violated the conscience that He's given to each one of us. (Rev. 21:8)
But imagine yourself back in that courtroom with a $500,000 fine on your head, and you don't have 2 nickels to rub together. They are leading you out of the courtroom to prison for the rest of your life when someone you don't even know comes into the courtroom and puts a $500,000 check on the judge's bench. Your debt has been satisfied and you are free to go. How would you feel about that person?
That's what God did for you. He gave his only Son, Jesus Christ, to die on the cross to pay the fine for your sins. He paid a debt He didn't owe because you owed a debt you couldn't pay. It's a free gift offered to anyone who will receive it. It does require more of you than just believing that Jesus existed and died on the cross. Even the devil believes that.
If you were on an airplane that was going down and you had a parachute under your seat, what would you do? It wouldn't do you any good to just believe that the parachute exists, and to sing songs to it on Sunday. You have to put it on for it to do you any good. The Bible says to put on the Lord Jesus Christ and you will be saved. You do that by putting your faith in Jesus Christ the same way you would that parachute. Then you repent of your sins, turning your back on them. You won't be perfect, but God will give you a new power over sin.
You don't need me or anyone else to tell you what to pray. Think of it this way: you are a man who has just committed adultery, and your wife is willing to forgive you, how do you reconcile the relationship? You humble yourself and tell her how truly sorry you are. No one would have to write it out for you. It would come from the heart, and that's what God wants from you. So, pour your heart out to Him, it's your heart, not the words, that matters. Then put your faith in Him the same way you do a pilot when you get on an airplane. Then read your Bible daily, obey what you read, and God will never fail you.